1. Field of the Invention
The present invention relates to an optical cross-connect apparatus disposed in an optical network and capable of outputting input wavelength division multiplexing light from a desired output port on the basis of a wavelength group or a wavelength.
2. Description of the Related Art
An optical network is known that transmits wavelength division multiplexing (WDM) light acquired by multiplexing a plurality of wavelength paths formed by combining optical signals of a predetermined bit rate on the order of GHz to THz for each of a plurality of wavelengths respectively corresponding to a plurality of wave channels (or light paths) divided by, for example, 100 GHz in a predetermined wavelength range from a predetermined optical node to a plurality of other optical nodes through pluralities of optical input fibers (e.g., m fibers) and optical output fibers (e.g., n fibers) (the number of fibers may be constant or inconstant between optical nodes) in a concurrent manner among the optical nodes. The number of the optical input fibers, for example, m, includes the number of optical fibers from a plurality of optical nodes, and the number of the optical output fibers, for example, n, includes the number of optical fibers to a plurality of optical nodes. In such an optical network, an optical cross-connect apparatus making up each optical node performs routing of wavelength division multiplexing optical signals transmitted through optical fibers on the basis of a wavelength directly in the form of optical signals, thereby implementing high-capacity transmission with low power consumption. For example, this corresponds to an optical cross-connect apparatus described in Japanese Laid-Open Patent Publication No. 2008-252664.
Since a traffic amount is predicted to increase at an accelerated rate in optical networks due to the recent spread of ADSL and FTTH and the spread of services such as distribution of high-definition moving images, it is desired to increase the numbers of wavelength paths and optical fibers, i.e., to further increase a scale of the optical cross-connect apparatuses making up the optical nodes.
Although, for example, the conventional optical cross-connect apparatus described in Japanese Laid-Open Patent Publication No. 2008-252664 uses a wavelength-selecting switch (WSS) in its configuration, the scale thereof is limited up to about 1-by-20 and a large-scale optical cross-connect apparatus is difficult to configure. Specifically, the wavelength-selecting switch (WSS) used in the optical cross-connect apparatus is functioned as, for example, a wave separator by employing a configuration selecting a wavelength from wavelength division multiplexing light by using a diffraction grating dispersing the light output from one end surface of a plurality of optical fibers, a condensing lens condensing the light dispersed by the diffraction grating onto MEMS mirrors of the same number as the separated wavelengths, and a three-dimensionally configured spatial optical system causing the light selectively reflected by the MEMS mirrors to be incident on one of end surfaces of a plurality of optical fibers through the condensing lens and the diffraction grating and, therefore, since the increased number of output ports not only makes the wavelength-selecting switch expensive because of the necessity of high-precision processing but also causes a greater increase in optical loss, the largest number of the ports is limited up to about 20 in existing wavelength-selecting switches, and it is practically difficult to implement a larger scale of the optical cross-connect apparatus. Although a 1-by-9 wavelength-selecting switch is frequently used in reality, even this requires a cost of about one million yen per switch.
For example, respective optical cross-connect apparatuses depicted in FIGS. 16, 17, and 18 are proposed for the optical nodes. An optical cross-connect apparatus OXC of FIG. 16 is configured based on a wavelength-selecting switch and, for example, when the number d of adjacent optical nodes is four, the optical cross-connect apparatus OXC includes 4m 1-by-4n wavelength-selecting switches WSS disposed respectively for 4m optical input fibers Fi1 to Fi4m and selecting a wavelength toward an arbitrary optical output fiber of a plurality of (4n) optical output fibers Fo1 to Fo4n from the wavelengths making up wavelength division multiplexing light from each of the optical input fibers Fi1 to Fi4m, and 4n 4m-by-1 wavelength-selecting switches WSS disposed respectively for a plurality of the (4n) optical output fibers Fo1 to Fo4n and combining and outputting a group of wavelengths output respectively from the 4m 1-by-4n wavelength-selecting switches WSS to a desired optical output fiber to which the group of wavelengths are directed out of a plurality of the (4n) optical output fibers Fo1 to Fo4n. The optical cross-connect apparatus OXC depicted in FIG. 16 has the 4m-by-1 wavelength-selecting switches WSS configured in the same way as the 1-by-4n wavelength-selecting switches WSS and used in the opposite direction, and is configured into a symmetric structure capable of fulfilling the same function even if input/output is reversed. An optical cross-connect apparatus OXC depicted in FIG. 17 is configured in the same way as the optical cross-connect apparatus OXC depicted in FIG. 16 except that the 4m 1-by-4n wavelength-selecting switches WSS are made up of 4m photocouplers PC. An optical cross-connect apparatus OXC depicted in FIG. 18 is configured in the same way as the optical cross-connect apparatus OXC depicted in FIG. 16 except that the 4n 4m-by-1 wavelength-selecting switches WSS are made up of 4n 4m-by-1 photocouplers PC. Although the number of input fibers from an adjacent node or output fibers to an adjacent node is uniformly m or n in the example of this description, a value of m or n may be different for each adjacent node.
If the optical cross-connect apparatus switches a route on the basis of a wavelength group or switches a route on the basis of a wavelength, for example, when it is assumed that the number m of the optical input fibers Fit to Fi4m is 28 and that the number n of the output fibers Fo1 to Fo4n is 28, the 28-by-28 optical cross-connect apparatus OXC depicted in FIG. 16 requiring the 4m 1-by-4n wavelength-selecting switches WSS and the 4n 1-by-4m wavelength-selecting switches WSS requires 56 1-by-28 wavelength-selecting switches WSS; the 28-by-28 optical cross-connect apparatus OXC depicted in FIG. 17 requiring the 4m 1-by-4n photocoupler apparatuses and the 4n 1-by-4m wavelength-selecting switches WSS requires 28 1-by-28 wavelength-selecting switches WSS; and the 28-by-28 optical cross-connect apparatus OXC depicted in FIG. 18 requiring the 4m 1-by-4n wavelength-selecting switches WSS and the 4n 1-by-4m photocoupler apparatuses requires 28 1-by-28 wavelength-selecting switches WSS.
Since a larger scale of the 1-by-28 wavelength-selecting switches WSS is difficult to create, for example, the 28 1-by-28 wavelength-selecting switches WSS in the optical cross-connect apparatuses OXC depicted in FIGS. 17 and 18 may be configured by using four realistic 1-by-9 wavelength-selecting switches WSS for each switch as depicted in FIG. 8, for example. The wavelength-selecting switch WSS depicted in FIG. 8 is 1-by-33 and is utilized as required and used as a 1-by-28 switch.
However, even the configuration requires as many as 4×28, i.e., 112, 1-by-9 wavelength-selecting switches WSS as a whole and causes a high cost of about 112 million yen, which is less practical.